Integrated heat management of electronics and fuel cell power system

ABSTRACT

A method and apparatus for managing heat generated by a device that is powered at least in part by a direct oxidation fuel cell. Additional heat tends to improve the reaction in the direct oxidation fuel cell, and so unwanted heat produced by a powered device can be harnessed to increase the temperature of the reaction in the direct oxidation fuel cell. By doing so, the performance of the fuel cell can be enhanced and the temperature of the heat-generating portion of the device maintained.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to the field of fuelcells and, more specifically, to a thermal management system thatintegrates a direct methanol fuel cell (DMFC) system and a device, inwhich the device is powered at least in part by the DMFC.

[0003] 2. Background Information

[0004] Fuel cells are devices in which an electrochemical reaction isused to generate electricity. A variety of materials may be suited foruse as a fuel depending upon the materials chosen for the components ofthe cell. Organic materials, such as methanol or natural gas, areattractive choices for fuel due to their high specific energy.

[0005] Direct oxidation fuel cell systems may be better suited for anumber of applications in smaller mobile devices (e.g., mobile phones,handheld and laptop computers), as well as in some larger applications.Typically, in direct oxidation fuel cells, a carbonaceous liquid fuel inan aqueous solution (typically aqueous methanol) is introduced to theanode face of a membrane electrode assembly (MEA). The MEA contains aprotonically-conductive, but electronically non-conductive membrane(PCM). Typically, a catalyst which enables direct oxidation of the fuelon the anode is disposed on the surface of the PCM (or is otherwisepresent in the anode chamber of the fuel cell). Diffusion layers aretypically in contact with at least one of the catalyzed anode andcathode faces of the PCM to facilitate the introduction of reactants andremoval of products of the reaction from the PCM, and also serve toconduct electrons. Protons (from hydrogen found in the fuel and watermolecules involved in the anodic reaction) are separated from theelectrons. The protons migrate through the PCM, which is impermeable tothe electrons. The electrons thus seek a different path to reunite withthe protons and oxygen molecules involved in the cathodic reaction andtravel through a load, providing electrical power.

[0006] One example of a direct oxidation fuel cell system is a directmethanol fuel cell system or DMFC system. In a DMFC system, methanol inan aqueous solution is used as fuel (the “fuel mixture”), and oxygen,preferably from ambient air, is used as the oxidizing agent. There aretwo fundamental half reactions that occur in a DMFC which allow a DMFCsystem to provide electricity to power consuming devices: the anodicdisassociation of the methanol and water fuel mixture into CO₂, protons,and electrons; and the cathodic combination of protons, electrons andoxygen into water. The overall reaction may be limited by the failure ofeither of these reactions to proceed to completion at an acceptable rate(more specifically, failure to oxidize the fuel mixture will limit thecathodic generation of water, and vice versa).

[0007] Typical DMFC systems include a fuel source, fluid and effluentmanagement systems, and a direct methanol fuel cell (“fuel cell”). Thefuel cell typically consists of a housing, and a membrane electrodeassembly (“MEA”) disposed within the housing. A typical MEA includes acentrally disposed protonically conductive, electronicallynon-conductive membrane (“PCM”) such as Nafion®, a registered trademarkof E. I. Dupont de Nours and Company, which is a cation exchangemembrane comprised of perfluorosulfonic acid, in a variety ofthicknesses and equivalent weights. The PCM is typically coated on eachface with an electrocatalyst such as platinum, or platinum/rutheniummixtures or alloy particles. On either face of the catalyst coated PCM,the MEA typically includes a diffusion layer. The diffusion layersfunction to evenly distribute the liquid and gaseous reactants to, andtransport the liquid and gaseous products of the reactions from thecatalyzed anode face of the PCM, or the gaseous oxygen from air or othersource across the catalyzed cathode face of the PCM. The diffusionlayers also facilitate the collection of electrons and conduction to thedevice being powered. In addition, flow field plates may be placed onthe aspect of each diffusion layer that is not in contact with thecatalyst-coated PCM to provide mass transport of the reactants and byproducts of the electrochemical reactions and also have a currentcollection functionality to collect and conduct electrons through theload.

[0008] One problem with electronic systems and components, includingthose which may be powered by DMFC systems, is that electroniccomponents and subsystems can become overheated, and their performancecompromised. This problem is especially difficult to effectively addressin small mobile devices where electronic components are packed tightlytogether and space, weight, and volume are critical design criteria. Insuch devices, it is desirable to minimize the number of componentsdedicated to cooling the system. Also, as mobile devices become morepowerful and require more power, mobile device components produceincreasing amounts of heat. Accordingly, it is increasingly important toremove heat from the electronic components and systems.

[0009] DMFCs are efficient at dissipating heat that is generated withinthe system, due to the fact that there are several fluids present in thesystem, and due to the fact that air is exchanged within the fuel cellsystem, allowing for a more natural heat exchange. In addition, thedirect oxidation fuel cell systems and DMFCs demonstrate increasedcurrent generation (at a given voltage) at higher temperatures due tothe increased kinetics of the reactions. Thus, if additional heat isapplied to the reaction, the DMFCs can become an even more suitablepower source.

[0010] It is thus an object of the invention to provide a thermalmanagement system that provides temperature regulation of a devicepowered at least in part by a DMFC system, in which excess heat producedby the device is transferred to the DMFC. As a result of this heattransfer, the temperature of the device is kept within a desired rangeand the operation of the DMFC is improved.

SUMMARY OF THE INVENTION

[0011] In brief summary, the present invention provides a thermalmanagement system that integrates a direct methanol fuel cell system anda device which is powered at least in part by the DMFC system. Theinvention provides the ability to transfer heat from the device to theDMFC system, which results in at least two benefits: the operatingtemperature of the device is regulated, and the DMFC's performance isenhanced.

[0012] In a first embodiment, the DMFC or some of its components areplaced in contact with the device, allowing for the conduction of heatfrom the device to the DMFC. This is preferably achieved by placing atleast one aspect of the housing of the DMFC system in direct contactwith the device or by passing reactants close to the device before thereactants are reacted within the DMFC. A similar approach based on heattransfer via a small fluid gap, wherein heat is transferred through airor a “thermal grease” is also contemplated. In a second embodiment,thermally conductive components are preferably integrated into thedevice to transfer heat from the device to the DMFC system, allowingbetter heat transfer.

[0013] In a third embodiment, air may be directed over the device beforeintroduction to the cathode face of the DMFC, depending on the desiredheat or humidity characteristics. If air is directed over the devicebefore introduction to the cathode face, it will remove heat from theheat generating electronics and increase the operating temperature ofthe DMFC, and tend to improve the kinetics of the reaction and the fuelcell system.

[0014] In a fourth embodiment, a pump in the DMFC is preferably used tocirculate a dedicated coolant (i.e. not one of the reactants) throughthe device. The coolant removes heat produced by the device andtransfers it to the DMFC where the heat is applied to the reactants.

[0015] In a fifth embodiment, a heat pump is used to transfer heat fromthe device, which heat is used in turn to vaporize the reactants. Thevaporized reactants are condensed within the DMFC system prior to beingreacted, thereby transferring heat to the DMFC.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention description below refers to the accompanyingdrawings, of which:

[0017]FIG. 1 is a block diagram of a direct methanol fuel cell systemknown in the prior art;

[0018]FIG. 2A is a schematic representation of fluid flow within thedevice powered by a fuel cell system;

[0019]FIG. 2B is a block diagram of a direct methanol fuel cell system,constructed in accordance with a preferred embodiment of the presentinvention, in which heat generated by an device is regulated inaccordance with the invention;

[0020]FIG. 3A is a perspective diagram of a device in which both thedirect methanol fuel cell system powering the device and aheat-generating portion of said device are enclosed by a common housing;

[0021]FIG. 3B is a perspective diagram of a device in which the directmethanol fuel cell system powering the device and a heat-generatingportion of said device are enclosed by discrete housings;

[0022]FIG. 4 is a block diagram of a direct fuel cell system in which athermally conductive material is used to manage heat generated by adevice;

[0023]FIG. 5A is a block diagram of a direct methanol fuel cell systemin which heat generated by a device is managed by transferring heat tofuel circulated in proximity to the device;

[0024]FIG. 5B is a block diagram of a direct methanol fuel cell systemin which heat generated by a device is managed by transferring heat to adedicated coolant circulated in proximity to the device;

[0025]FIG. 6 is a block diagram of a direct methanol fuel cell system inwhich heat generated by a device is managed by transferring heat to aircirculated through device;

[0026]FIG. 7 is a perspective drawing of a circuit board in which heatis managed by conduction through a conduit running over the processor,carrying reactants to the direct methanol fuel cell or a pump, or adedicated coolant to the pump;

[0027]FIG. 8A is a perspective drawing of a circuit board in which heatis managed by conduction in which a conduit carries reactants to thedirect methanol fuel cell or a pump, or a dedicated coolant to the pump;

[0028]FIG. 8B is a perspective drawing of a circuit board in which heatis managed by conduction through a conduit running under a processormounted on the circuit board;

[0029]FIG. 9 is a perspective drawing of a circuit board in which heatis managed by conduction through a conduit running around the sides ofthe processor;

[0030]FIG. 10 is a block diagram of a direct methanol fuel cell systemin which heat is managed by a heat pump/valve.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

[0031] An example of a direct oxidation fuel system 20 is schematicallyillustrated in FIG. 1. The fuel cell system 20 includes a directoxidation fuel cell, which may be a direct methanol fuel cell 21(“DMFC”), for example. For purposes of illustration, and not by way oflimitation, we herein describe an illustrative embodiment of theinvention with DMFC 21, or DMFC system with the fuel substance beingmethanol or an aqueous methanol solution. However, it is within thescope of the present invention that other carbonaceous fuels such asethanol, or combinations of carbonaceous fuels and aqueous solutionsthereof may be used. It should be further understood that the inventionis applicable to any fuel cell system where it is preferable tointroduce a liquid fuel or component thereof to the anode aspect 26 ofthe membrane electrode assembly (MEA) 25 and not simply the embodimentsdescribed in FIG. 1.

[0032] The system 20, including the DMFC 21, has a fuel delivery systemto deliver fuel from fuel source 22. The DMFC 21 includes a housing 23that encloses a MEA 24. MEA 24 incorporates protonically conductive,electronically non-conductive, membrane (PCM) 25, and typically includesat least one diffusion layer in contact with one or both aspects of thePCM 25. PCM 25 has an anode face 26 and cathode face 27, each of whichmay be coated with a catalyst, including but not limited to platinum, ora blend of platinum and ruthenium. Diffusion layers are usuallyfabricated from carbon cloth or carbon paper that are treated with amixture of Teflon® and high surface area carbon particles, are typicallyprovided and in intimate contact with the catalyzed faces of each of theanode 26 and cathode 27 aspects of the PCM 25, though the invention isnot limited to systems that require diffusion layers. The portion ofDMFC 21 defined by the housing 23 and the anode face 26 of the PCM 25 isreferred to herein as the anode chamber 28. The portion of DMFC 21defined by the housing 23 and the cathode face 27 of the PCM 25 isreferred to herein as the cathode chamber 29. The anode chamber 28 andcathode chamber 29 may further contain a flow field plate or plates (notshown) in contact with the diffusion layer, in order to manage the masstransport of reactants and products of the reaction. Those skilled inthe art will recognize that the catalyst may be applied to the PCM 25 byapplying a suspension containing the catalyst to PCM 25. As used hereinthe terms “anode face” and “cathode face” may refer to the catalyzedfaces of the PCM 25, and shall include any residual catalyst materialsthat may remain on the surface of the PCM 25 as the result of suchapplication.

[0033] As will be understood by those skilled in the art,electricity-generating reactions occur when a carbonaceous fuel mixture,including, but not limited to methanol or an aqueous methanol solutionis introduced to the anode face 26, and oxygen, usually from ambientair, is introduced to the cathode face 27. More specifically, acarbonaceous fuel mixture from fuel source 22 is delivered by pump 30 tothe anode chamber 28 of the DMFC 21. The fuel mixture passes throughchannels in the flow field plate (or is present in the anode chamber28), and/or a diffusion layer, and is ultimately presented to the anodeface 26 of the PCM 25. Catalysts on the membrane surface (or which areotherwise present within the MEA 24) enable the anodic oxidation of thecarbonaceous fuel on the anode face 26, separating hydrogen protons andelectrons from the fuel and water molecules of the fuel mixture. Uponthe closing of a circuit, protons pass through PCM 25, which isimpermeable to the electrons. The electrons thus seek a different pathto reunite with the protons, and travel through a load 31 of an externalcircuit, thus providing electrical power to the load 31. So long as thereactions continue, a current is maintained through the externalcircuit. Direct oxidation fuel cells produce water (H₂O) and carbondioxide (CO₂) as products of the reaction, which must be directed awayfrom the catalyzed anode and cathode membrane surfaces 26, 27. The gasseparator 32 separates the excess air and water vapor from the water.This water can be later directed to the pump 30 via a flow path 33.Those skilled in the art will recognize that the gas separator 32 may beincorporated into an existing component within the DMFC 21 or the DMFCsystem 20.

[0034]FIG. 2A shows a more general schematic representation of the flowof the reactant from the fuel source 22 over the heat-generating portion46 of the device, prior to delivering the reactant to the DMFC 21.

[0035]FIG. 2B shows an electronic device 40 which is powered at least inpart by a direct methanol fuel cell system 62 placed in contact with orproximity to heat generating portion 46 of the device 40, thus enablingthe conduction of heat from portion 46 to the DMFC 42 or relatedcomponents. The DMFC system 62 may also include a battery, capacitor orother power storage device (not shown). Electronic device 40 mayrepresent, for example, a wireless phone, notebook computer or any of avariety of other devices, which may be powered by a fuel cell. In thisillustrative embodiment, some or all of a housing 52 of the DMFC 42, agas separator 44, and conduits 47-50 and 53 that direct both the flow ofreactants to the DMFC 42 and the flow of products from the DMFC 42 arepreferably placed in direct contact with or in proximity to the portion46. By placing conduits 47-50 and 53 in contact with or in proximity toportion 46, the conduits may conduct heat from portion 46, therebyheating the reactants flowing through the conduits. A similar approachbased on convection may be used as well, as heat may be transferred fromportion 46 to the DMFC 42 or related components indirectly.

[0036]FIGS. 3A and 3B show different configurations of a device poweredat least in part by a DMFC system 62. In FIG. 3A, a single housing 64contains both the DMFC system 62 powering the device 64 and theheat-generating portion 46 of said device 64, as well as othercomponents which provide functionality. In FIG. 3B, the DMFC system 62is not enclosed in the same housing that encloses the device 68. Thereare just two of many possible configurations recognizable to thoseskilled in the art. These figures are for illustration and not intendedto limit or proscribe any possible couplings of the heat-generatingportion of a device to the DMFC system.

[0037]FIG. 4 shows a second embodiment of the present invention in whicha thermally conductive material 61, preferably made of a polymer butother materials such as metal could be used as well, is positionedbetween DMFC 42 (and possibly related components) and heat-generatingportion 46, allowing for the transfer of heat from the portion 46 toDMFC 42. Those skilled in the art will appreciate that conductivematerial 61 may be placed in contact with some or all of othercomponents (pump 43, gas separator 44, various conduits) in order toachieve a desired heat transfer rate, packaging requirements or otherrequirements of a particular application. Though the DMFC system 62 andthe heat-generating portion 46 are shown as being in contact on a singleplane, those skilled in the art will recognize that the interface maytake place on more than one aspect between the heat generating portion46 and the fuel cell system 62. Those skilled in the art will furtherrecognize that the heat conducting material 61 may simply be comprisedof an air gap and/or a “thermal grease”.

[0038]FIG. 5A shows a third embodiment in which a conduit 71 between thefuel source 41 and the pump 43 is routed in proximity to heat-generatingportion 46. Conduit 71 is preferably arranged in an elongated,serpentine configuration such that it presents a large surface area forheat transfer between heat generating portion 46 and the fuel in theconduit 71. The transferred heat increases the temperature of the fuelflowing in conduit 71, thus effectively transferring heat to DMFC 45.Conduit 71 may alternatively be placed in direct contact with portion46, similar to FIG. 2. Conduit 71 is in substantially the same plane asthe portion 46, though there may be instances where the conduit 71extends along more than one aspect of the portion 46. Those skilled inthe art will recognize that it is possible to implement conduitscontaining water or other reactants in a substantially similar fashion.Other variations include, but are not limited to, eliminating the gasseparator 44, or anode fuel and recirculation components (conduits 50and 53) so that the heat is conducted to the fuel after it leaves thefuel source 41 but before it enters the fuel cell 42. FIG. 5B shows analternative embodiment in which fuel is delivered directly to a pump 82which circulates a fluid through the heat-generating portion 46 inconduit 81. The fluid may be either; 1) a reactant; or 2) a dedicatedcoolant utilizing a separate, closed loop system (not shown) and may beused to absorb heat from the heat generating portion 46 and transmit itto the DMFC 42 after passing through conduit 81. The fluid is eventuallyreturned to the pump 82 where heat may be transferred to the reactantsthat pass into the DMFC 42, or if the fluid is a reactants it may bedelivered to the DMFC 42.

[0039]FIG. 6 illustrates a fourth embodiment in which air passes througha conduit 91 in proximity to heat-generating portion 46, allowing heatto be transferred to the air before it is introduced to the DMFC 42.Like in the embodiment of FIG. 5A, a serpentine configuration of conduit91 is preferable as this increases the surface area available for heattransfer, though other configurations are also within the scope of theinvention. This embodiment may require a component to assist in airinduction, such as a fan (not shown) to increase the volume of air thatpasses through the cathode chamber of the fuel cell 42. By introducingwarmer air into the cathode of the DMFC 42, the kinetics of the cathodicreaction is enhanced, and performance of the DMFC 42 is increased.

[0040] It is further possible to integrate the fluidic components withthe heat-generating portion 46 of the device, if the DMFC system and theportion are mechanically integrated. FIGS. 7, 8A, 8B and 9 showdifferent arrangements of conduits 102, 110, 111 or 112 passing inproximity to heat-generating components. In FIG. 7, conduit 102 passesover a processor 104, which is connected to a printed circuit board 106by leads 108. Heat produced by the processor 104 is transferred to theconduit 102, which in turn transfers heat to the fluid flowing throughthe conduit 102 en route to or from the DMFC (not shown). In FIG. 8A,conduit 110 passes under processor 104. In FIG. 8B, conduit 111 passesunder processor 104 in a channel or saddle 107 in the printed circuitboard 105. In FIG. 9, conduit 112 passes around the sides of processor104. In FIGS. 7-9 reactants may be routed though conduits 102, 110, 111and 112 before being routed to the pump (not shown) or to the DMFC (notshown). Alternatively, a dedicated coolant may be routed throughconduits 102, 110, 111 and 112.

[0041]FIG. 10 shows a fifth embodiment in which a simple heat pump/valve122 is used to assist is pumping vaporized reactants to DMFC 121. Heatis transferred from the heat-generating portion 46 to the heatpump/valve 122, which in turn transfers heat to the reactants enteringthe heat pump/valve 122 via conduit 123. This may result in thereactants being vaporized, after which they are routed to the DMFC 121via conduit 124. The vaporized reactants then condense, or are reactedin vapor phase, within the DMFC 121 prior to being reacted, therebytransferring heat to the DMFC 121.

What is claimed is:
 1. A method for managing heat generated by a devicethat is powered at least in part by a direct oxidation fuel cellcomprising the steps of: providing a device that is powered at least inpart by said direct oxidation fuel cell system, said fuel cell systemincludes an anode, a cathode, a housing, and at least one source ofreactants; and transferring at least a portion of the heat generated bysaid device to said fuel cell, whereby an operating temperature of saiddevice is regulated and an operating temperature of said fuel cell israised.
 2. The method of claim 1 further comprising the step of:arranging said fuel cell and said device so that said heat transfer issubstantially conductive.
 3. The method of claim 1 further comprisingthe step of: arranging said fuel cell and said device so that said heattransfer substantially takes place through an air gap or a thermallyconductive material.
 4. The method of claim 1 further comprising thestep of: transferring at least some of said heat to reactants beforereacting said reactants in said fuel cell.
 5. An apparatus for managingheat generated by a device that is powered at least in part by a directoxidation fuel cell comprises: a direct oxidation fuel cell coupled toprovide power to said device; and means for managing heat generated bysaid device such that at least some of said heat is transferred fromsaid device to said fuel cell, whereby an operating temperature of saiddevice is regulated and an operating temperature of said fuel cell israised.
 6. The apparatus of claim 5 wherein said means for managing heatfurther comprises: a thermally conductive material placed between aheat-generating portion of said device and said fuel cell such that saidmaterial is in contact with some or all of the components of saidheat-generating portion.
 7. The apparatus of claim 5 wherein heat fromsaid device is transferred to said fuel prior to entering said directoxidation fuel cell.
 8. The apparatus of claim 5 wherein heat from saiddevice is transferred to the oxygen source prior to oxygen from saidsource entering said direct oxidation fuel cell.
 9. The apparatus ofclaim 5 wherein said means for managing heat further comprises: a fuelsource; a pump; and a conduit coupling said fuel source to said pump,said conduit arranged so as to transfer heat from a heat-generatingportion of said device to fuel flowing in said conduit prior tointroduction of said fuel into said fuel cell.
 10. The apparatus ofclaim 5 wherein said means for managing heat further comprises: a pump;and a conduit coupled to said pump and arranged to circulate a dedicatedcoolant so as to transfer heat from a heat-generating portion of saiddevice to said fuel cell.
 11. The apparatus of claim 5 wherein saidmeans for managing heat further comprises: an air source; and a conduitcoupling said air source to said fuel cell, said conduit arranged so asto transfer heat from a heat-generating portion of said device to airflowing in said conduit prior to introduction of said air into said fuelcell.
 12. The apparatus of claim 5 wherein said means for managing heatfurther comprises: a fuel source; a conduit coupling said fuel source tosaid fuel cell; and a heat pump, connected along said conduit, fortransferring heat produced by a heat-generating portion of said deviceto fuel carried by said conduit, whereby said fuel is vaporized prior tointroduction into said fuel cell.
 13. The apparatus of claim 5, whereinsaid means for managing heat further comprises: means for transferringheat substantially by conduction.
 14. The apparatus of claim 5, whereinsaid means for managing heat further comprises: means for transferringheat substantially across an air gap or through a thermally conductivematerial.
 15. The apparatus of claim 5, said means for managing heatfurther comprises: means for transferring heat substantially by usingone or more said fuel cell's reactants.
 16. The apparatus of claim 5,wherein said means for managing heat further comprises: means fortransferring heat substantially by using one or more said fuel cell'sproducts.
 17. An apparatus for managing heat generated by a device thatis powered at least in part by a direct oxidation fuel cell comprises: adirect oxidation fuel cell coupled to provide power to said device; anda thermally conductive material arranged so as to transfer at least someof heat produced by a heat-generating portion of said device to saidfuel cell, whereby an operating temperature of said device is regulatedand an operating temperature of said fuel cell is raised.
 18. Anapparatus for managing heat generated by a device that is powered atleast in part by a direct oxidation fuel cell comprises: a directoxidation fuel cell coupled to provide power to said device; a pump; anda conduit coupled to said pump and arranged to circulate a dedicatedcoolant so as to transfer at least some of heat produced by aheat-generating portion of said device to said fuel cell, whereby anoperating temperature of said device is regulated and an operatingtemperature of said fuel cell is raised.
 19. An apparatus for managingheat generated by a device that is powered at least in part by a directoxidation fuel cell comprises: a direct oxidation fuel cell coupled toprovide power to said device; an air source; and a conduit coupling saidair source to said fuel cell and arranged so as to transfer at leastsome of heat produced by a heat generating portion of said device to theair flowing in the conduit prior to introduction into said fuel cell,whereby an operating temperature of said device is regulated and anoperating temperature of said fuel cell is raised.
 20. An apparatus formanaging heat generated by a device that is powered at least in part bya direct oxidation fuel cell comprises: a direct oxidation fuel cellcoupled to provide power to said device; a conduit coupling said fuelsource to said fuel cell; and a heat pump, connected along said conduit,for transferring at least some of heat produced by a heat-generatingportion of said device to fuel carried by said conduit, whereby saidfuel is vaporized prior to introduction into said fuel cell, anoperating temperature of said device is regulated, and an operatingtemperature of said fuel cell is raised.
 21. A method for managing heatgenerated by a device that is powered at least in part by a directoxidation fuel cell comprising the steps of: providing a device that ispowered at least in part by said direct oxidation fuel cell system, saidfuel cell system includes an anode, a cathode, a housing, and one ormore sources of reactants; and transferring at least a portion of theheat generated by said device to said fuel cell, whereby an operatingtemperature of said device is lowered and the temperature of at leastone of said reactants is raised prior to introduction into the fuel cellsystem.
 22. The method of claim 19 further comprising the step of:arranging said fuel cell and said device so that said heat transfer issubstantially conductive.
 23. The method of claim 19 further comprisingthe step of: arranging said fuel cell and said device so that said heattransfer is substantially convective.
 24. An apparatus for operating adirect oxidation fuel cell that powers, at least in part, a device,comprising: a direct oxidation fuel cell coupled to provide power tosaid device, said direct oxidation fuel cell having improved operationperformance in response to an increase in its operating temperature; andmeans for transferring heat from said device to said direct oxidationfuel cell for raising said operating temperature.
 25. The apparatus ofclaim 22 in which said transfer means comprises: means for transferringheat generated by said device to reactants of said direct oxidation fuelcell before said reactants are introduced to said direct oxidation fuelcell.
 26. A portable device powered at least in part by a directoxidation fuel cell, said device having an operating temperature whichis at least partially regulated by transferring heat generated by saiddevice to at least one of a plurality of reactants used by said fuelcell.